Exploring stress level-dependent true constrained modulus in sand with dynamic hammer testing

This study employs the Dynamic Hammer (DH) test to assess the constrained modulus ( ) of sand compacted within a modified California Bearing Ratio (CBR) mold specifically designed for bulk stress measurement. The DH test facilitates the measurement of bulk stress ( ) activated during the test. Conventional analytical methods often underestimate the  value due to bedding errors at the interface between the loading plate and the sand’s top surface. This research introduces novel test methods and analyses to obtain the accurate constrained modulus ( ) within the designed CBR mold. The DH test involved variations in sample height (H) at 125, 177.8, and 228 mm, and falling height (h) at 2, 4, 6, and 8 cm, resulting in different levels of . The  value derived from the DH test (M_DH) was utilized to establish  relationships for different H values. Subsequently, these relationships were further analyzed to derive the  relationship. A comparison was then made between the  and  relationships derived from a separate series of one-dimensional compression tests. The  value was adjusted by comparing it with the results of triaxial compression tests, where a local technique for axial strain measurements was employed to minimize the influence of bedding errors. Key findings indicate that  and  increase with rising . When compared at the same ,  significantly surpasses due to bedding errors. Interestingly, and  values exhibit notable similarity. This research contributes valuable insights into accurately assessing the constrained modulus of sand within a unique CBR mold designed for bulk stress measurement.